Gas Hydrate Research Articles

Undrained triaxial tests of underconsolidated overlying sediments of hydrate deposits in the South China Sea

The South China Sea (SCS) is an important repository for natural gas hydrates (NGHs), where some NGH deposits and their overlying sediments (OSs) are in an underconsolidated state. During the exploitation of NGHs, the stability of the OSs of the NGH deposits is one of the key factors in ensuring mining safety. Especially under different consolidation degrees, the mechanical response and stability of the OSs will vary, which directly affects the safety and efficiency of the NGH mining. This research explores the influence of different consolidation degrees on the mechanical properties of the OSs of NGH deposits in the SCS. The strength and pore pressure characteristics were analyzed through undrained triaxial shear tests. The findings indicate that an increase in consolidation degree enhances the strain softening behavior, and an increase in initial effective stress enhance the strain hardening and shear contraction behaviors of the samples. The failure strength, modulus, and maximum excess pore pressure increase with the consolidation degree and initial effective stress, and there is an approximately linear correlation between failure strength and consolidation degree. Therefore, the exploitation of NGHs in the SCS must comprehensively consider the burial depth and consolidation degree of the OSs. The findings of this study will assist in optimizing mining plans and enhancing safety during the exploitation process.

Experimental study on the effect of hydrate saturation in reservoir on microwave heating hydrate decomposition gas production

Microwave heating technology is an effective method to promote the decomposition of hydrates, with hydrate saturation being an important parameter influencing this process. This study has synthesized natural gas hydrates with different saturations within a high-pressure reaction vessel to conduct experiments on the decomposition of natural gas hydrates by microwave heating. The reservoir temperature, gas production dynamics, and energy utilization rate are investigated for hydrate saturations of 30.26 %, 35.63 %, and 39.61 %, respectively. The results indicate that increasing hydrate saturation enhances the microwave penetration depth, which in turn elevates the reservoir temperature and accelerates hydrate decomposition. When the hydrate saturation increases from 30.26 % to 39.61 %, the gas production time decreases. Simultaneously, both the volume and rate of gas production increase, accompanied by enhanced energy utilization rate. When the hydrate saturation is 39.61 %, the experiment achieves an average gas production rate of 1.17 L/min, a total volume of 19.73 L, and an energy utilization rate of 2.716. The research results can promote the application of microwave heating technology in the development of hydrates.

Experimental Study on Memory Effect of Gas Hydrates: Interaction between Micronanobubbles and Solute Molecules

Experimental Study on Memory Effect of Gas Hydrates: Interaction between Micronanobubbles and Solute Molecules

Constraints on Characteristics and Distribution of Gas Hydrate and Free Gas Using Broad-Band Processing of Three-Dimensional Seismic Data

Constraints on Characteristics and Distribution of Gas Hydrate and Free Gas Using Broad-Band Processing of Three-Dimensional Seismic Data

Insights into the dual effect of an amphiphilic additive on hydrate formation from a water structure perspective

Chemical additives play an important role in gas hydrate formation, which involves the transformation of water structure. However, the relationship between the effects of additives on water structure and hydrate formation is inconclusive, especially for amphiphilic molecules. Here, we investigate the changes in water structure caused by rhamnolipid (Rha) biosurfactants and the resulting effect on methane hydrate formation through kinetic experiments, morphological observation, and in situ Raman spectroscopy. The Gaussian peaks of strongly hydrogen-bonded and weakly hydrogen-bonded water are identified, of which the integrated intensity and position are compared. It is found that the dual effect of Rha on hydrate formation kinetics, namely nucleation inhibition and growth promotion, is attributed to the ordered arrangement of water molecules with stronger hydrogen bonding interactions induced by the charged head groups. The strongly hydrogen-bonded water inhibits nucleation but promotes growth. In addition, the adsorption of Rha on montmorillonite (MMT) eliminates the changes in water structure and the dual effect of hydrate formation kinetics, providing further evidence for the above conclusion. These insights pave the way for a deeper understanding of hydrate formation kinetics from a water structure perspective, as well as providing a scientific basis for the commercial application of surfactants.

Storage and Transportation of Hythane: Thermodynamics, Kinetics, and Stability Studies Using the Gas Hydrates Process

Storage and Transportation of Hythane: Thermodynamics, Kinetics, and Stability Studies Using the Gas Hydrates Process

Experimental study on gas hydrate generation in a thermal-kinetic binary promotion system

ABSTRACT The primary measure for the prevention and control of coal and gas protrusion is gas extraction. However, various factors, such as coal seam conditions, drilling construction, and extraction management, have led to poor gas management. Therefore, the method of transforming gaseous gas into solid hydrate provides a new direction for the prevention and control of coal and gas herniation. In this paper, the factors that influence gas hydrate solidification and its influence law are explored. A thermo-kinetic binary promotion system was constructed by combining thermo-kinetic promoters, and experiments on gas hydrate generation under the thermo-kinetic binary system were carried out. The effects of four thermodynamic accelerators (CP, THF, TBAB, HCFC-141b) compounded with the kinetic accelerator SDS on the gas hydrate generation characteristics were determined. The experimental results show that among the four thermodynamic promoters, THF and SDS have the best synergistic effect, and the optimal mass concentration ratio of the two is 21.2 wt% THF + 8.6 wt% SDS. The gas pressure in the reactor decreased by a maximum of 2.788 MPa within 500 min in this experimental system, and the absorption rate of gas reached 55.41%, which indicates a more pronounced hydration promotion effect.

Super-resolution reconstruction of hydrate-bearing CT images for microscopic detection of pore

The pore structure of marine natural gas-hydrate-bearing sediments is a key factor related to the physical properties of reservoirs. However, the resolution of micro-computed tomography (micro-CT) images is unsuitable for the analysis of pore structures in fine-grained sediments. In this regard, super-resolution (SR) reconstruction technology is expected to improve the spatial resolution of micro-CT images. We present a self-supervised learning method that does not require high-resolution datasets as input images to complete the training and reconstruction processes. This method is an end-to-end network consisting of two subnetworks: an SR network and a downscaling network. We trained on a self-built dataset of hydrate samples from three different particle sizes. Compared with typical methods, the SR results indicate that our method provides high resolution while improving clarity. In addition, it has the highest consistency with the liquid saturation method with the subsequent calculation of porosity parameters. This study contributes to the investigation of seepage and energy transfer in sediments containing natural gas hydrates, which is particularly important for the exploration and development of marine natural gas hydrate resources.

Molecular insights into methane hydrate dissociation: Role of methane nanobubble formation.

Understanding the underlying physics of natural gas hydrate dissociation is necessary for efficient CH4 extraction and in the exploration of potential additives in the chemical injection method. Silica being "sand" is already present inside the reservoir, making the silica nanoparticle a potential green additive. Here, molecular dynamics (MD) simulations have been performed to investigate the dissociation of the CH4 hydrate in the presence and absence of ∼1, ∼2, and ∼3nm diameter hydrophilic silica nanoparticles at 100bar and 310K. We find that the formation of a CH4 nanobubble has a strong influence on the dissociation rate. After the initial hydrate dissociation, the rate of dissociation slows down till the formation of a CH4 nanobubble. We find the critical concentration and size limit to form the CH4 nanobubble to be ∼0.04 molefraction of CH4 and ∼40 to 50 CH4 molecules, respectively. The solubility of CH4 and the chemical potential of H2O and CH4 are determined via Gibbs ensemble Monte Carlo simulations. The liquid phase chemical potential of both H2O and CH4 in the presence and absence of the nanoparticle is nearly the same, indicating that the effect of this additive will not be significant. While the formation of the hydration shell around the nanoparticle via hydrogen bonding confirms the strength of interactions between the water molecules and the nanoparticle in our MD simulations, the contact of the nanoparticle with the interface is infrequent, leading to no explicit effect of the nanoparticle on the dynamics of methane hydrate dissociation.

Influence of CO2 injection rate and memory water on depressurization-assisted replacement in natural gas hydrates and the implications for effective CO2 sequestration and CH4 exploitation

This study was conducted to investigate the influence of CO2 injection rate and memory water on guest exchange and hydrate reformation behavior in CH4 hydrate-bearing sediment, using a one-dimensional (1-D) reactor to optimize depressurization-assisted replacement. Increasing the CO2 injection rate facilitated the rapid sweeping of CH4 into the pore space of the hydrate-bearing sediment, inducing immediate hydrate reformation and preventing CH4 re-enclathration in the middle region of the 1-D reactor. Despite dissociating 50 % of the initial CH4 hydrate for depressurization-assisted replacement, the replacement efficiency converged at around 70 % due to drastically reformed gas hydrates hindering mass transfer. Introducing time intervals between depressurization and replacement to reduce the residual memory effect of water led to delayed hydrate reformation, altering the longitudinal distribution of replacement efficiency in the 1-D reactor. An increase in replacement efficiency toward the outlet was seen, suggesting that improved CO2 propagation in the hydrate-bearing sediment resulted in a higher CO2 concentration in the vapor phase at the point of hydrate reformation, in turn enhancing CO2 storage efficiency in the newly formed hydrates. These experimental results highlight the importance of CO2 injection rates and time intervals in determining the hydrate reformation behaviors of hydrate-bearing sediments and optimizing the efficiency of depressurization-assisted replacement.

Rapid hydrogen enclathration and unprecedented tuning phenomenon within superabsorbent polymers

Clathrate hydrate has emerged as a potentially viable storage medium for efficient hydrogen storage, owing to its eco-friendly characteristics and high hydrogen storage capacity. However, it is essential for its practical application to address the challenges posed by harsh thermodynamic formation conditions and slow formation kinetics for hydrogen hydrate. Here, we introduce the utilization of superabsorbent polymers (SAPs) as a dispersion matrix for tetrahydrofuran (THF) solutions to develop a method for rapid hydrogen enclathration. We investigated two distinct synthetic pathways, solution-borne and hydrate-borne routes. We also explored the relationship between hydrogen uptake/storage capacity, varying THF solution concentration within SAPs, and synthetic pathways for binary THF–hydrogen hydrates. The hydrogen storage capacity after 200 min enclathration reaction was relatively low for 1.0 mol% THF cases but significant for 5.56 mol% THF cases in hydrate-borne route (around 20 mmol H2/mol water), highlighting its potential for hydrogen storage material. The spectroscopic analysis revealed that the tuning phenomenon in THF 1.0 mol% hydrate was only observed in the solution-borne route, which facilitated hydrogen enclathration in partially vacant large cages of sII hydrates. It was striking that the tuning phenomenon was also observed in THF 5.56 mol% hydrate synthesized in both solution-borne and hydrate-borne pathways. Through phase equilibria measurements, we confirmed that less than 5.56 mol% of THF participated in forming binary hydrates. The different water and THF absorbability of SAPs resulted in a non-uniform distribution of THF solution within SAPs, causing the unprecedented tuning phenomenon. These findings provide valuable insights into the potential of SAPs for rapid hydrogen enclathration media, emphasizing the importance of understanding synthetic pathways and solution absorption properties for optimized hydrogen storage.

Interactions of clathrate hydrate promoters sodium dodecyl sulfate and tetrahydrofuran investigated using 1H diffusion nuclear magnetic resonance at hydrate-forming conditions.

Thermodynamic hydrate promoters and kinetic hydrate promoters can be used to reduce the P-T conditions for clathrate hydrate synthesis to decrease the nucleation induction time while increasing growth rates. Two commonly used promoters for hydrate research are tetrahydrofuran (THF) and sodium dodecyl sulfate (SDS), which can increase the overall hydrate promotion when used in tandem as compared to individually. There are several molecular theories regarding how SDS promotes hydrate growth. This study explores the micellular theory, for which hydrate formation depends on surfactant aggregates (micelles) at a critical micelle concentration (CMC) to increase the interfacial surface area. The micellular theory is the most investigated and criticized surfactant hydrate promotion theory. To address questions related to micellar behavior, this study investigates the intermolecular behavior between SDS and THF for the identification of micelles at hydrate-forming conditions. The systems explored contained THF at 3 and 5 wt. % with varying concentrations of SDS below and above the CMC. Several methods including a qualitative visual method, conductivity, interfacial tensiometry, 13C Liquid-state Nuclear Magnetic Resonance (NMR) spectroscopy, and 1H diffusion NMR spectroscopy were evaluated at temperatures below the Krafft point of SDS and above 0 °C. The presence of THF at low concentrations decreased the critical temperature for the formation of SDS micelles, where SDS is solubilized in THF/water solution at hydrate-forming temperatures without precipitation. The CMC of SDS was decreased significantly even at hydrate-forming conditions. Mixed surfactant-cosolvent micellular behavior of SDS in the presence of low concentrations of THF was confirmed at hydrate-forming conditions above 0 °C.

EXPERIMENTAL STUDY OF HYDRATE FORMATION PECULIARITIES FOR CONDITIONS OF THE TURNO AND CENOMANIAN DEPOSITS: Part II

This paper is the second part of the research devoted to the study of hydrate formation features for the conditions of Turonian and Cenomanian deposits. The launch of new gas projects at the Turon and Senoman production facilities in Western Siberia provided a good opportunity to critically analyze the known methods of protecting production, gathering and transportation facilities of the gas field from the formation of solid gas hydrates. The paper presents the experience of implementing a program of laboratory studies of conditions of gas hydrate formation with their subsequent processing and in-depth analysis. The research program covered the area of thermobaric parameters typical for the conditions of Turon-Senoman deposits exploitation with localization of hydrate-hazardous areas in the conditions of Technological Regimes for full development. The description of laboratory studies is given, in which two gas compositions of Senoman and Turon objects, different variants of mineralization and ionic composition corresponding to formation and condensation water, as well as hydrate formation conditions under changing dosages of basic inhibitor on the basis of methanol were considered. The details of the experiment based on the method of swinging cells and the subsequent analysis of the results of the completed experiments to determine the thermobaric conditions of formation and decomposition of hydrates are given. The main features of the experiment are specified, estimates of the rate of change of the influencing parameters of the experiment on its quality are given. In the process of implementation of the experimental program, the optimal values of these parameters were selected, which allowed us to significantly reduce the variation of experimental results to determine the thermobaric conditions of hydrate formation. It is experimentally established that the temperature of hydrate decomposition is higher than the temperature of its formation at all investigated gas compositions and water mineralization.

Formation Kinetics and Morphology Characteristics of Fracture-Filling Natural Gas Hydrate under the Influence of Multiple Parameters

Formation Kinetics and Morphology Characteristics of Fracture-Filling Natural Gas Hydrate under the Influence of Multiple Parameters

Natural gas hydrate dissolution kinetics in sandy sediments: Implications for massive water production in field tests

The tremendous natural gas hydrate (NGH) reserve in globe makes it a promising future energy. The field test production indicates that massive water production may occur in the depressurization of sandy NGH reservoirs. The dissolution of NGH may play a significant role in this process. Therefore, quantifying the NGH dissolution kinetics and clarifying the relations between NGH dissolution and water production is crucial. In this work, a modified excess water method was developed to prepare quasi-homogenous water-saturated methane hydrate (MH) bearing sediments (HBS). The MH dissolution kinetics were investigated by flowing methane-free water through the HBS. The MH dissolution process could be divided into the rapid stage and the decayed stage. Preferential flow channels may form by the inhomogeneous MH dissolution. Water flux has a significant impact on the MH dissolution kinetics via affecting the mass transfer and the hydrate-water exposure in flow channels. When increasing the water fluxes from 2.0 mL·cm−2·min−1 to 6.1 mL·cm−2·min−1, the MH dissolution rate initially ramped up from 15.4 cm·d−1 to 36.0 cm·d−1 (mass transfer dominates), and then decreased to 28.7 cm·d−1 (flow channels dominate). MH saturation has an influence on dissolution kinetics. The MH dissolution rate increased from 27.1 cm·d−1 to 44.2 cm·d−1 when the MH saturations increased from 11.8 % to 60.1 %. Experimental results indicate that the preferential flow channels by inhomogeneous NGH dissolution could contribute to the massive water production in the depressurization of NGH reservoir. Large pressure gradient in NGH production may accelerate the NGH dissolution and the following massive water production. Homogeneous high-saturation HBS could more facilitate the hydrate-water exposure for dissolution, which could retard the onset of massive water production. This work may ignite some new thoughts on the water control and production optimization strategies in sandy NGH exploitation.

Source-to-sink processes and genetic mechanism of progradational and lateral accretion submarine fans in the Qiongdongnan Basin, South China Sea

Submarine fan reservoirs are important accumulation zones for oil, gas, and natural gas hydrates, offering significant potential for hydrocarbon exploration. During the deposition period of the Sanya Formation in the southern part of the Changchang Sag of the Qiongdongnan Basin, a large submarine fan developed. However, the internal structure, source-sink system, and formation mechanism of this fan remain poorly understood, posing significant challenges to exploration in this area. This paper examines the source-to-sink sedimentary processes and deposition of submarine fans, using the Changchang Sag, in the Qiongdongnan Basin in the Northern South China Sea, as an example, which will provide valuable general guidance for deep water oil and gas exploration. Based on the theories of seismic stratigraphy and seismic sedimentology, this paper utilizes techniques such as seismic facies analysis, seismic attribute optimization, paleogeomorphology reconstruction, and source-to-sink sedimentary system analysis to analyze the 3D seismic data of the study area. Research indicates that the Sanya Formation in the Changchang Sag of the Qiongdongnan Basin comprises three depositional units: submarine fan, feeder channel, and Semi-deep marine to deep marine mudstone. The submarine fan is a fan formed by the coupling and convergence of submarine fans sourced from the southwest and southeast. Internally, it is divided into three sub-facies: the proximal fan of the sand-rich submarine fan, the main body of the sand-rich submarine fan lobes, and the distal lobes of the sand-rich submarine fan. The submarine fan sourced from the southwest extends nearly north-south and is primarily fed by sediment transported through three large, banded ancient valleys. The sedimentary filling is characterized by three-phase progradation. The submarine fan sourced from the southeast extends nearly east-west and is primarily fed by sediment transported through a single large, banded ancient valley. The sedimentary filling is characterized by two-phase lateral accumulation. During the deposition period of the Sanya Formation, certain areas of the southern uplift belt were exposed for extended periods and subjected to weathering and erosion. Sediments are transported to large ancient valleys through small supply channels. A large number of sediments were transported to the southern slope of the Changchang sag through the provenance channel system such as large ancient valleys and slope belts and deposited in the center of the sag. These make up a complete system of large ancient uplifts and submarine fan source-to-sink sedimentary systems.The sedimentary model is a lobed submarine fan controlled by semi-restricted ancient valleys and expansive basins.

Significance of well placement and degree of hydrate reserve recovery for synergistic CH4 recovery and CO2 storage in marine heterogeneous hydrate-bearing sediments

The synergistic CH4 recovery and CO2 storage in marine natural gas hydrate reservoirs presents an emerging strategic solution for energy and environment challenges, yet the efficiency requires innovative engineering designs to enhance. In this study, a water-saturated CH4 hydrate-bearing sediment (HBS, V = 22 L, T = 284 K, and P = 11.2 MPa) was synthesized to investigate the pilot-scale combined processes of CH4 recovery by depressurization followed by CO2 storage through CO2/N2 injection. The synthesized HBS exhibited vertical heterogeneity with higher hydrate saturation observed in the upper sediment and a decreasing saturation trend in the lower sediment. The effect of well placement designs on CH4 recovery and hydrate restoration by mixed CH4/CO2/N2 hydrate (Mix-H) formation was investigated, considering two scenarios: upper well for recovery while lower well for injection (URLI), and lower well for recovery while upper well for injection (LRUI). Additionally, the impact of the degree of hydrate reserve recovery (100% and 80% hydrate dissociated) on subsequent Mix-H formation was also studied. Results indicate that the URLI setting achieves a higher CH4 recovery ratio and rate during depressurization compared to the LRUI setting which encounters low-T shielding. The T variation between upper and lower sediment highlights the influence of heterogeneity on fluid behaviors. Halting the CH4 recovery after 80% hydrate dissociation results in a halved recovery time and water production. During later CO2/N2 injection and Mix-H formation process, the LRUI setting achieves a 13–54% higher Mix-H saturation and a 33–56% higher CO2 hydrate encapsulation than the URLI setting. Moreover, 80% dissociation proves more favorable for Mix-H formation achieving nearly twice higher final amount than 100% hydrate dissociation. However, it results in a lower CO2 encapsulation. This study provides insights into the trade-off between CH4 recovery and CO2 storage efficiency, emphasizing the need for optimized well placement and controlled hydrate extraction.

Gas hydrate technological applications: From energy recovery to carbon capture and storage

Hydrates are crystalline structures that trap small gas molecules inside hydrogen-bonded water cages. These structures form at high pressure and low temperature. In recent years, there has been a growing interest in gas hydrates for technological applications, specifically in energy recovery, as well as carbon dioxide capture and storage. In the CO2/CH4 exchange using gas hydrates, researchers have reported a large amount of natural gas trapped in the form of gas hydrates under the ocean seafloor and permafrost regions. This large amount of natural gas trapped inside hydrate cages in oceanic and permafrost deposits has driven interest in the energy sector to investigate the possibility of safely harvesting gas hydrates as one of energy resources. However, there are still unanswered fundamental questions including the mechanism of natural gas recovery from gas hydrates. Another gas hydrate-based technology that has a growing interest is the use of gas hydrates for separation including carbon dioxide capture and storage. Carbon dioxide molecules have been shown to be preferentially trapped in the hydrate phase, demonstrating the possibility of the usage for carbon capture technology. Similarly, there are still underlying concerns of these applications, such as thermodynamics and stability of gas hydrates in porous materials, and the crystallization kinetics and mechanism of hydrate formation. This paper provides an overview of laboratory investigations conducted to understand the mechanism and evaluate the feasibility of energy recovery as well as discussion on recent advances in laboratory investigations on gas hydrate-based technology.

Dynamics of Horizontal Well Drilling in Deepwater Shallow Gas Hydrate Reservoirs: A Mass and Heat Transfer Study

Summary Natural gas hydrates represent a promising and environmentally friendly alternative energy source, with horizontal wells being an effective method for efficient extraction. However, the drilling process of horizontal wells presents challenges due to the prolonged contact between the drilling fluid and the hydrates. This interaction leads to a significant influx of drilling fluid, triggering hydrate phase transition and causing instability within the wellbore. To address these technical issues, this study focused on decomposition-induced wellbore instability and reservoir structure damage during deep-sea natural gas hydrate drilling. Specifically, we investigated the stability of the gas hydrate phase during drilling shallow, deep-sea horizontal wells. To accomplish this, we established a 2D mathematical model that describes the nonsteady-state mass and heat transfer process between the wellbore and hydrate reservoir. In addition, we explored the mass and heat transfer mechanisms between the drilling fluid and hydrates, obtaining a 2D distribution of temperature and pressure fields within the wellbore and hydrate reservoir. The findings of this research contribute to the theoretical and technical development of safe and efficient drilling fluids for hydrate reservoirs.

Long-Term Distributed Temperature Sensing Monitoring for Near-Wellbore Gas Migration and Gas Hydrate Formation

Summary Well integrity monitoring has always been a critical component of subsurface oil and gas operations. Distributed fiber-optic sensing is an emerging technology that shows great promise for monitoring processes, both in boreholes and in other settings. In this study, we present a case study of using distributed temperature sensing (DTS) technology to monitor a cemented and plugged well in the Alaska North Slope (ANS). The well was drilled as part of a long-term gas hydrate study, and the downhole DTS data were recorded over a period of approximately 2 years. By applying a temporal gradient and removing instrument instability noise, we reveal subtle (<0.001°C/h) thermal anomalies, which are characterized by brief warming periods followed by longer cooling periods at discrete depths along the borehole. The observed coherent events show an upward trajectory from deeper formations into the overlying permafrost interval, with the thermal anomalies concentrated in relatively coarse-grained sandstone layers. We also observe that the upward migration rate of the DTS anomalies varies with formation lithology and that there is a spatial and temporal correlation between the subsurface events and measured wellhead annular pressures. We interpret that the observed warming events represent the exothermic process of gas hydrate formation that is occurring in association with the upward migration of gas outside the well casing, and this interpretation is confirmed by numerical simulations. These observations demonstrate the ability of suitably processed DTS data to detect subtle processes and highlight the value of DTS technologies for wellbore integrity monitoring.